Door Testing Furnace for Fire proof ness

Offhand the size 3M x 3M sound insufficient. IIRC, limits for fire rated door/window assemblies in USA and Canada are closer to 5M wide x 4M tall. If you cannot test and certify assemblies at least as large as other label agencies, you may be quite limited in your potential.

[edit] If testing criteria only calls for door to be tested swinging out, the 800 mm might be okay. If you need to burn with the door swinging in, the 800mm is very likely insufficient.

I am assuming these tested doors are pedestrian doors.

It is assumed you are aware that a fire door burn test is a hot messy smelly loud violent affair.

It is further assumed that a hose stream test (simulating a direct spray fire hose) is at the end of the burn. I can tell you, this phase of a burn test is an especially hot messy smelly steamy loud violent affair.

Without any test criteria, it is difficult to offer useful suggestions.